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yr 10 physics > waves 2 > Flashcards

waves 2 Flashcards

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1
Q

Radio waves

A

type of electromagnetic wave with the longest wavelength

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2
Q

Wavelength of radio waves

A

greater than 30 cm

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3
Q

How are radio waves produced

A

by passing an oscillating current through a long wire called the aerial

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4
Q

what does the frequency of the radio wave depend on

A

same as the frequency of the oscillating current

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5
Q

radio waves of different wavelengths have…

A

different properties

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6
Q

are radio waves absorbed strongly by the walls

A

no so radio wave signals can be received indoors

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7
Q

radio waves in transmitters

A

Sound waves are turned into oscillating crrent and then radio waves in an eariel

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8
Q

radio waves receivers

A

picked up by aerails radio waves turned into oscillating current and then into sound waves

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9
Q

why can some radio waves travel so far?

A 
low-frequency( up to 3Mhz) radio waves can travel hundreds of miles and they travel on earth s surface. Ground waves can be used for local and national radio
Higher frequency (3-30 MHz) radio waves reflected from the ionosphere. These sky waves are used for international and amateur radio.
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10
Q

Wireless network

A

Wi-fi allows us to acees the internet without any wires. It uses high frequencies that are around 2.4GHz. Wi-fi can be connected through access points and the area that they cover is the hotspot. They can be unreliable as they only cover up to 100m.

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11
Q

Microwaves

A

Electromagnetic radiation and are shorter wavelength radio waves

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12
Q

wavelength of microwaves

A

from 30 cm to 1mm

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13
Q

How are microwaves produced

A

Long-wavelength microwaves are madde using an aerial similar to radio waves and are used fro communication
Shorter wavelength microwaves are made by a device named megnetron and are used in microwave ovens and radar equipment

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14
Q

size of antennas

A

radio antennas are large because radio waves wavelength is high but a phone s antenna is small as microwaves have smaller wavelengths. For optimal efficiency, the antenna should be as large as the carrier wave’s wavelength.

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15
Q

How does my mobile phone work

A

Network providers divide the area into cells and at the center of each cell is a base. Your phone sends and receives microwaves so it is a 2-way radio. These microwaves come and go at different frequencies so you can talk and hear what the other person is hearing. Once you get a weak signal from a base your phone connects to another base that gives a better signal.

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16
Q

what effects my mobile phone reception

A

different factors but microwaves loose intensity as they travel so distance is also a factor. Furthermore, if there are tall buildings and create pockets without reception so low power transmitters are used to fill in the gaps.

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17
Q

microwaves and staellite communication

A

they are very high-frequency (30MHz) radio waves so they are not reflected by the ionosphere but refracted thus they can be picked up by satellites and amplified and then transmitted into different countries very far away.

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18
Q

ALARA priceiple preacutions

A

using a hand-free kit or shield
limit time taking on the phone
Using phone that emits less radiation
Under 16s use phones when essential

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19
Q

experiment if hand free is going to make a difference

A

IV: distance from transmitter to receiver
DV: Intensity of microwaves depending on the distance
Results: as distance increases the intensity of microwaves decreases.

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20
Q

how much are mobile phones mass threat to our health

A

masts are less likely to release less radiation than phones

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21
Q

amplification

A

strength of a signal

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22
Q

base station

A

equipment at the center of the cell that receives and transmits signals.

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23
Q

visible light wavelength

A

390nm to 780nm, different wavelengths equate to different colours in the spectrum

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24
Q

how is light produced

A

emitted by very hot objects, filament in a bulb is 2500 degrees celsius, in the sun nuclear fusion occurs to create light and in neon lights a current passes through gas to produce light.

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25
Q

light and computers

A

computers code digital signals that can be used to send in optical fibres

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26
Q

infrared waves

A

from of electromagnetic radiation that we experience everyday

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27
Q

wavelength of IR

A

from 1mm to 0.0001mm

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28
Q

How is IR used in remotes

A

Not all IR is thermal, short-wavelength IR are not hot and cannot be detected by the skin. Type of IR used to send signal by remotes over short distances in the air. This way IR can only go in a straight line but we can use optical fibres for IR to travel long distances and go around corners

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29
Q

Digital remote control signals

A

Different signals are sent when u tap on different buttons of the remote

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30
Q

total internal reflection

A

normally when a light ray hits a boundary between different density objects it refracts. This is due to the change in speed. If the angle of incidence ray is greater than a value called the critical angle then the right is reflected and it works like it is a perfect mirror. Called internal reflection.

31
Q

Why angle of incidence is important

A

When the angle of incidence is smaller than the critical angle then the light ray is refracted.
If the angle of incidence is = to critical angle the light ray is refracted along the boundary.
If the angle of incidence is bigger than the critical angle total internal reflection happens where light rays are reflected and it works like a mirror.

32
Q

Critical angle

A

the smallest angle of incidence at which total internal reflection occurs

33
Q

Optical fibers

A

thin strands of solid glass. Can transmit light signals at high speeds at long distances.

34
Q

Optical fibers in medicine

A

Can be used to see inside the patient without cutting them open. A device used for this is called an endoscope and a bundle of optical fibers is in it. Some fibers carry light down and then light reflected and comes back from the other fibers.

35
Q

Why don’t messages get mixed up in optical fibers

A

Multiplexing is the method for sending lots of messages without them getting mixed up

36
Q

What are 2 types of multiplexing

A

Wavelength division

Time division

37
Q

Multiplexing: wavelength division

A

Each message sent at different wavelengths and the receiver tunes into the wavelength of the message

38
Q

Multiplexing: time division

A

Each message is divided into chunks for transmission. Messages are put back at the other end.

39
Q

analogue

A

a signal with continual varying signals

40
Q

attenuation

A

loss of strength of a signal during transmission

41
Q

X- rays

A

form of electromagnetic radiation with very short wavelength and are very high in energy so are strongly ionizing.

42
Q

X-rays wavelength

A

0.01 to 10nm

43
Q

how are x-rays made

A

very fast moving electrons are suddenly stopped and where collisions happen when stopped created x-rays and often are created in x-ray tubes

44
Q

stages in taking x-rays

A

X-ray tube is switched on , x-rays from tube pass through patient’s body.

A photographic film or a flat –panel detector is placed on the other side of the patient

X-rays pass through soft tissue, but absorbed by bones, teeth and metals objects that are not too thin.

The parts of the film or detector panel, where the x-rays get through to, become darker. Therefore, bones, teeth, etc, appear white in comparison.

Lead plates between the tube and patient stop x-rays reaching other parts of body. Lead is used as it absorbs x-rays well.

A flat- panel detector contains a ‘charge-coupled device’ (CCD). This turns x-rays into light, which in turn create electronic signals, to produce a digital x-ray image.

45
Q

situations of x-ray stages

A

If the organ being investigated (x-rayed) is made of soft tissue (like the stomach), the x-rays will normally go through it, instead of being absorbed.

In that case the organ is filled with a contrast medium – something which will absorb the x-rays so those parts stand out more clearly in a radiograph.

E.g. before a stomach x-ray, patient will be given a barium meal – which is good at absorbing x-rays.

46
Q

what safety precautions taken for x-rays: patients

A

are given as small a dose as possible
have radiation targeted only at the area of the body being imaged or treated
have other areas protected with a lead shield, which is too dense for X-rays to pass through.

47
Q

what safety precautions taken for x-rays: Radiographers

A

are high-risk as they are exposed to radiation often
wear a lead apron
stand behind a screen that absorbs X-rays
or even leave the room.

48
Q

Using radiation to treat cancer

A

Radiotherapy is the use of high-energy ionizing radiation, such as X-rays and gamma rays, to kill cancer cells.
In external-beam radiotherapy, a concentrated beam of short-wavelength X-rays or gamma rays (cobalt -60) is targeted at cancerous cells from a radiation source outside the body.

49
Q

Radiotherapy

A

Gamma rays can kill cancer cells, but are also dangerous to healthy cells
We need to target the gamma rays (and high energy x-rays) to the cancer very precisely so that the radiation dose to healthy tissue is kept to a minimum.
In particular we need to avoid any nearby organs such as eyes or spinal cord.
A medical physicist decides which angles to shine x-rays from
to destroy tumour and minimise damage to other tissue

50
Q

how are gamma rays produced

A

When un unstable nucleus undergoes radioactive decay. Normally an alpha or beta particle is released (with or without EM waves like gamma rays)

51
Q

What are the types of doses

A

Alpha
Beta
Gamma

52
Q

Radiation dose

A

The radiation dose received by a person is a measure of the damage done to their body by ionizing radiation.

53
Q

What does radiation dose depend on

A

Type of radiation used
How long body is exposed to radiation
The energy per second absorbed by the body from the radiation.

54
Q

What is radiation dose measured in

A

Sieverts(SV) and millisieverts(mSV)

55
Q

Dangers of the EM spectrum

A

the smaller wavelength waves can interact with cells and can be ionising

56
Q

UV radiation from the sun

A

The Sun emits Ultraviolet (UV) radiation
UV waves have enough energy to damage cells
Overexposure to UV can cause sunburn or even skin cancer

57
Q

Sunburn and skin cancer

A

Sunburn is a painful sign that UV is damaging you

Skin cancer is cause by molecules in damaged cells dividing rapidly, forming a tumour

58
Q

Who is at higher Risk from skin cacer

A 
are fair skinned and burn quickly 
have freckles and/or moles 
were frequently exposed to the sun as children 
suntan deliberately 
have a family history of skin cancer 
work outdoors for long periods of time 
use solariums, sunlamps and sunbeds.
59
Q

Who is less risk of skin cancer

A

People with darker skins
Dark skins contain a pigment called melanin which absorbs UV and prevent it reaching the underlying tissue (live skin cells in body tissues under skin)

People with easily tanned skin
Weak exposure to UV over a few days can cause fair skins to tan, because the body produces a black pigment called melanin in the skin.

People who take steps to protect themselves from UV radiation.

60
Q

How to avoid sunburn

A

Shade
one of the most effective ways to protect against the sun’s UV rays
Clothing
provides a barrier between UV rays and the skin.
Hats
The correct type of hat shades the face, eyes and neck
Sunglasses
UV rays can also damage eyes
Sunscreen
should be the last method of sun protection.

61
Q

Ozone layer

A

The ozone layer is a layer in Earth’s atmosphere (13-40km up) which contains relatively high concentrations of ozone (O3).
This layer absorbs 97–99% of the sun’s high frequency ultraviolet rays, which is potentially damaging to life on earth.

62
Q

How are x-ray produced in x-ray tubes

A

Electrons from the hot cathode are fired at the tungsten target at high speed. When these high-energy electrons strike the target, some of their energy is changed into X-rays.

63
Q

How x-rays look inside objects

A

x-rays pass through soft tissue, such as skin and muscle, without being absorbed. Denser tissue, such as bone, can absorb X-rays. Film that is exposed appears black and areas that are not exposed, because of X-ray absorption, are white.

64
Q

Some uses of x-rays

A

X-rays are used in medicine and in security to check the contents of baggage and vehicles for weapons, drugs and other contraband.

65
Q

X-rays intensity

A

They loose strength because they are absorbed by denser mediums

66
Q

Unobvious signs of x-ray imagings

A

Computer Aided Tomography scans (CAT or CT scans) use static X-ray images taken from lots of angles to build up 3D pictures of internal organs.
A special type of X-ray imaging machine called a fluoroscope acts as an X-ray video camera. A moving X-ray image of internal organs is shown on a TV screen.

67
Q

What precaution i taken so cells do not get infected by radiotherapy

A

Radiation is shot from multiple angles

68
Q

Brachytherapy

A

In brachytherapy, an alpha or beta emitter is surgically implanted into the tumour or a nearby body cavity.
This can be used for tumours in sensitive areas, including breast, cervix and prostate cancer.

69
Q

systematic radioisotope therapy

A

In systematic radioisotope therapy, the isotope is injected into the blood stream. This is used to treat thyroid cancer and to provide palliative care when cancer is advanced.

70
Q

Advantages of external beam therapy

A

The beam can be moved and targeted at the tumour rather than at surrounding tissue.
Effective for tumours in the outer regions of the body.
Type of radiation: X-rays or gamma rays. These rays are strongly penetrative and can pass through soft tissues without being absorbed

71
Q

Advantages of internal radiation therapy

A

For some tumours, brachytherapy can give more intense radiation than external beam radiation, without harming healthy tissue. For example, external beam radiation treatment can cause skin irritation in the area exposed to the beam, which is avoided by internal radiotherapy.
Treatment with internal radiotherapy can usually be completed in less time than an equivalent course in external beam radiation, with fewer visits to the hospital for the patient.
If the tumour moves in the body, external beam radiation can be miscalculated and fail to target the tumour. However, brachytherapy implants retain their position relative to the tumour.
Effective for tumours which are surrounded by sensitive tissue or which are deep within the body so that radiation beams would have to pass through sensitive tissue in order to reach them.
Type of radiation: alpha or beta particles. These particles are not very penetrative and are mostly absorbed by tissues surrounding the source of the radiation. This makes them less dangerous for surrounding healthy tissues

72
Q

Disadvantages of external beam therapy and internal radio therapy

A

Fatigue and nausea are common side effects of all types of radiotherapy.
Side effects usually depend on the area treated by radiotherapy and the frequency and intensity of the radiation used.

73
Q

PET imagining

A

Positron Emission Tomography (PET) is a type of imaging which uses radioactive isotopes.
The isotope is injected, swallowed or breathed in. It is called a tracer. The isotope emits positrons through β+ decay, which annihilate electrons inside the body to produce gamma radiation.
The scanner detects the gamma rays and creates an image of the body on a screen. Doctors can use this to investigate body functioning, e.g. blood circulation or metabolism.

74
Q

Dose in PET imagining

A

The isostope is prepared in half-life in the hospital and have a very short period of decay but many hospitals fo not have the equipment for that.

yr 10 physics (1 decks)

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